Screw-propeller.



C. H. DRAPBR.

SCREW PROPELLER.

APPLICATION FILED 1.11m, 1910.

1,01 9,437. Patented Mar. 5, 1912.

2 SHEETS-SHEET 1.

mm. I g

0. H. DRAPER.

SCREW PROPELLBR.

APPLIOATION FILED JAN. 6, 1910. 1,01 9,437. Patented Mar. 5, 1912.

2 SHEETS-SHEET 2.

CLARE H. DRAPER,

OF HOPEDALE, MASSACHUSETTS, ASSIGNOR TO 0. F. ROPER &

COMPANY, OF HOPEDALE, MASSACHUSETTS, A FIRM.

SGREW-PROPELLEB.

Specification of Letters Patent.

Patented Mar. 5, 1912.

Application filed January 6, 1910.- Serial No. 536,688.

To all whom it may concern:

Be it known that I, CLARE H. DRAPER, a citizen of the United States, and resident of Hopedale, county of \Vorcester, State of Massachusetts, have invented an Improvement in Screw-Propellers, of which the folthe pitch of a propeller blade theoretically determines the axial distance traveled in one revolution, but as a matter .of fact a propeller working in water does nottravel such axial distance in one'revolution, by an amount designated the apparent slip.

The great majority of screw propellers are of uniform pitch at all points of the driving surfaceof the blade, and when so construct ed are termed true screw propellers, but in my present invention I depart from a true screw propeller in many particulars, some of which may in themselves be old, but so far as I am aware the combination of various features of construction in one blade is novel.

In my present invention I construct the blade of the propeller with an increasing axial pitch, 1n order that the leading edge of the blade as it enters the water shall not accelerate it in either direction, while the rest of the blade acts gradually upon the water and finally gives the maximum acceleration at the back or following edge of such'blade. Increasing axial pitch means thatthere is greater pitch on the back partor following edge of the blade thanon the leading edge thereof, the driving surface of the blade being necessarily somewhat concaved as compared to a true helical surface.

When it is considered that a propeller does not advance in accordance with its pitch it Wlll be evident that the blade of a true screw propeller must catch the water, at its,

leading edge and suddenly accelerate it 'by approximately as much as the slip. My novel propeller has an increasing radial pitch, that is,

the blade has greater pitch at the circumference than, at'the hub, this feature resulting or flowing from the embodiment of the various principles of construction in accordance with my invention.

In my improved propeller the blade presents what 1 term a centripetal surface, that is, a surface which is not only inclined with relation to the axial movement or direction of advance but which is also inclined backward from a radial plane at right angles to the propeller shaft. Such centripetal surface tends ro throw the water inward toward the axis of the shaft as well as to drive itbackward in columnar form. The blade of a true screw propeller imparts a centrifugal motion to the water acted. upon, leaving it so that such water tends to spread astern in the form of a cone, thereby reducing the reaction upon the boat which tends to push it. ahead. If a section of such a centripetal blade be taken in an intersecting plane at right angles to the axis of rotation the edge of the section will be a curve inclining from the hub portion of the blade outward in the direction of rotation of the propeller, and

herein such curved lines or edges I designate as the generating lines of the blade.

VVhen'laying out a blade in accordance. with my invention I prefer to make such generating lines tangent to radii atthe hub and increasing in curvature from the leading edge of the ing edge thereof. Such increase in the curvature of the generating lines is due to the fact that as the leading edge does not accelerate the water to any extent it will not cause much centrifugal action, and accordingly there is not so much necessity for counter-acting centrifugal action as there s at or near the following edge of the blade. Inasmuch as this portion of the blade is accelerating the water more than any other portion increased centripetal action is required, and consequently greater curvature, obtained by the increasing curvature of the generating lines, referred to.

My improved blade preferably has uniform pitch at the hub, for the reason that in a blade of increasing axial pitch the increasing curvature of the generating lines is permitted by but is not necessarily due to uniform pitch at the hub. At the hub the pitch is the same as at the leading edge 0 the blade, such surface performing practically blade to theback or followof the blade, and it is, consequently and D 1s cast I build up such necessarily, of less pitch than at any other point except the leading edge. The reason for using increasing .radial 'pi'tch hereinbefore referred to is thus made manifest, By having generating lines of lessicur'vatur e at the leading edge of the blade the latter is set more nearly at right angles to. the projpeller shaft than would be the case if all the generating lines were of the maximum curvature. This is advantageous in that the blade ispracticable for reversing propellers, which might not be true with a blade mclined aft to a marked degree.

I prefer to make my. improved propeller blade approximately elliptical in outline,

not, only because such asha e'is generally considered -to be the most e cient but-also qreasons pointed out. The leading edge of.

because the rounded ends of the blades are less apt to be bent or brokenwhen striking obstacles or tangled up in weeds, ropes, etc. Such centripetal blades as'have heretofore been devised are, so far as I have been able to discover, of a more or less hooked formcorresponding to the curves of the generating lines, and are. objectionable for the the blade I round off on the working surface instead of on the opposite or-forward side of the blade, as is the common practice, forby so doing I make it certain that all water acted upon byv the blade is forced astern, whereas-with the'common form a the boat and certain amount of water-and especially so with blades of axially increasing pitch-is forced ahead in the direction of travel of p y so much inevitably reduces the ropeller efficiency; 1 Figure-1 is a front'elevationof a screw propeller blade embodying my present invention, viewing the blade 'in a direction looking aft with r'elation'to the shaft or axis of rotation; Fig. 2 is-a top plan view of the. blade shown in Fig. 1, the large arrow indicating the direction of axial movement effected by revolution of the blade fromleft toright; Fi 3. is a right hand side elevation of the b ade, viewingFig. 1', and showisof jblade, taken on the lines A,'B, C, etc, Figs. 1 and 3; Fig. .5 is a; diagrammatic view I lates" .5 I

ingthe working side or face of such blade;

Fig. 4 are transverse sections through the showing the manner in which the generating lines are laid out for constructing a propeller blade in accordance with my inven- 'tion, Fig.6 is a diagram used in laying out t the generating'lines shown in Fi Tie; a" lan .view of one of the Ill anks or.

"fthe' other-and also showing the manner in which the generatin 'lines are used in'c'ompletin thepatternor the blade.

' To acilitate the construction of the pattern "having a length, fore and aft, or

.arcs b, c, the former indicating'theexternal cumference of the propeller, the radii of both arcs being determined according to v om which the pattern is built ups K 1g;. -8' 1 s' a sectional detail of the several plates or 1811111133, superimposed one upon tern for making the mold in which the blade attern from superposed and relatively tlnn wooden plates-or laminae, the forward edge of each plate being cut to a curve corresponding to one of. the generating lines, the plates or lamina) being glued '-or otherwise secured together. The length of the laminae is sufiicient to enable the blade of desired length to be cut therefrom, the hub portion of the blade pataxially, equal to the thickness of a plate multiplied by the number of such plates, as will be obvious,'though the length of such hub portion can be increased if necessary in anysuitable manner. Taking a point a, Fi 5, to represent the center or axis of rotation of the propeller I strike therefrom diameter of the hub and the latter the cirthe desired dimensions of the propeller. first'decide. at wha t distance from the center a I will take what I. call the base-line, and at which approximately the greatest width of the blade is to be, anddraw an are d with the radius decided upon, and on this are I lay off the distance d", 50, Fig. 5, equal to'the widthof the proposed blade as 'projected upon 'a plane at right angles to the axis of rotation of the propeller. Then -measuring the actual length d", 50, along the are d I lay this distance offat -51 on the horizontal line h, Fig. 6, and erect a perpendicular h 'at' 51. After deciding upon the average pitch along are a? and the pitch of the hub and leading edge of the blade I determine the angles corresponding ,to these pitches" and draw lines 72' and p passing through point 50 and making the determined angles with the horizontal line h, Fig. 6. The angle between p and k corresponds-"to the average pitch and the angle'betwe'en pand h-corresponds to the pitch of the leading .edge of the blade and .at the huh. I nowbisect that part of line p between its points of intersection with h and h and erect a perpendicular 53 at the center, and erect a perpendicular 55 to line 19 at the point 50. The intersection 54 of these two perpendiculars I takeas a center and describe thearc p", Fig. 6, passing through the points 50, )2 and to which the line p is' tangent at'150. This curved line 71* repre-' sents a section of the working surface of the h, Fig. 6, is divided into as many parts as' there are to be laminae-in the pattern, and

which practically corresponds to the length of the hub, and: the points ofdivisionare projected horizontally onto the curve p, as at 56, 5'T, *etc'. These intersection'sfare projected onto the base line It at 56*, 57, etc, as shown in Fig. 6, and it will be seen that the I blade along theline d, Fig. 5. Now the line the blade. obtalned are now laid off on the arc (1, Fig.

distances between successive points on the base line gradually decrease from right to left, indicative of an increase in axial pitch from the leading to the following edge of The divisions of the base line so 5, beginning at the point 50, the leading edge of the blade in said Fig. 5 being at the right hand, and the points thus laid off on arc (Z are similarly lettered. Radial lines '2', 1-, are now drawn through points and 56* and the center 1/, Fig. 5, such radii intersecting the arc Z) of the hub portion, and other radii '1', r etc., at the left, Fig.

are drawn to intersect the are I) equal distances apart, and equal to the distance between the first two radii 011 the said are. This must give the same pitch at the hub as between 50 and 56*, for it will be remeni bered that generating lines which. are straight and radial form a uniform pitch or true screw blade.

The varying pitch of the blade isnot necessarily due to the uniform pitch at the hub, for obviously the pitch at the hub may be an increasing or a decreasing pitch and yet permit of an increasing pitch at. the outer portion of the blade. Increasing or decreasing the pitch at the hub in this particular case interferes with or modifies the hook of the blade, in the one instance giving more hook at the leading edge, where itis not needed, and less at the following edge, where it is needed. while in the other instance the whole blade is given entirely too much hook, which is not desirable and which I desire to obviate. Uniform pitch at the hub enables me to secure the desired results,.and the in creased curvature of the centripetal surface is permitted, so it will be seen that the generating lines must intersect the are 7; at equal distances apart. I

It will be manifest that the blade embodying my invention is not a true screw blade, hence the generating lines cannot be the straight radii, but are curved lines, the first one to be laid off on Fig. 5 being determined to a very great extent by experience, such line determining the greatest amount of hook which is desired for the blade. The shorter the radius of such curved generating line tangent on theline I) to one of the radii pre-' viously drawn, and manifestly this center point must lie on a normal to the selected radius.

In Fig. 5 I have chosen to make the first generating line tangent at Z) to the radius 1',

hence the center point will lie on its normal 71. and the curved line I is the first generating line, which intersects the line (Z at the point Normals n is, a, etc., are laid otf from the respective radii at their intersections with the are 5, and in the present instance, circular arcs II, III, IV, etc. are struck from centers on the respective normals. passing through the previously found points. t", etc., to the point- 50, laid off on the arc 1/. and tangent to radii 9' '1', etc., at the hub. \Ye nowhave the necessary generating lines for the blade, and they are transferred to the front or leading edges of the wooden platcs'or laminae from which the pattern is built up, it being understood that viewing Fig. 5, the forward or non-working face of the blade would be nearer the observer. It must be understood that the actual angle of the generating line. I, at the line (Z, may vary slightly from the angle first chosen or fixed upon, as it is necessary to make the curve of the generating line I tangent to one of the radii at 7), but the variation. if there is any, is necessarily small. Inasmuch as the generating lines increase in curvature from the leading to the following edge, for reasons hcreinbefore set forth, it follows that successive generating lines laid out at the right of line I decrease in curvature, and the distance between the intersections of successive pairs of generating lines with the arc (Z gradually increases from left to right, according to the desired increasing axial pitch of the blade.

In Fig. 7 is shown one. of the blanks or plates M, in plan, its edge on having the curve of one of the generating lines, in this case the line V, Fig. 5, and the part M of the plate is the hub portion. After all of the plates have been shaped they are superposed and glued together, as shown in Fig. 8, and a warped and stepped surface is presented, which is cut down on each face to give the desired curvature to the surfaces of the blade.

Referring to Fig. 8, the working face of the .-bla de passes through the several points m", and when the working face has been completed the opposite face of the blade is completed similarly, depending of course upon the thickness of the'blade, and the particular curvature which the forward ornon-working face is to have. The building up of the pattern from laminae is well known in constructing patterns for propeller blades, and I make no claim thereto.

An inspection of Figs. 1. 2 and 3, showing the completed blade, (made from a pattern derived as has been described,) together withthe several sections of the blade shown in Fig. t will make clear the general contour and features of the blade constructed in accordance with my invention. The outline of the blade as shown in 5 is elliptical, for the reasons hereinbefore set forth,

- and such outline in Fig. 5is actually the pro- ,jection of the finished bladeupon a plane surface at right angles to the axis of rotation of the blade. The leading edge t-of the blade is rounded oi? on the working face or surface W, as at t", Fig. 3, while the opposite or forward. face F is brought directly to said leading "edge almost flat. This change is also clearly shown in the blade sections, Fig.4, the leadingedge of each section beingindic'ated at t.

The hub is indicated at H,- Figs.'l, 2 and 3, and in practice the flat face of the hub of each blade will be secured to the shaft, or a part carried thereby, in any suitable manner, as by bolts passed through the holes 20, Fig. 2, in the sockets 'H formed in. the

Having fully described my invention, what I claim as new and desire to secure by] Letters Patent is LA propeller blade having generating llnes for lts working surface increasing in curvature from the leading to the follow-J 1ng edge, said generating lines 'being tangent toradii at the periphery of the hub,

the pitch being uniforrn at the hub.

2. A propeller blade whose working surface has generating lines increasing in curvature from the leading to the following to radii at the periphery of the hub and 1ying wholly between such radii and the leadmg edge.

In testimonywhereof, I have signed my name to this specification, in the presence of two subscribing Witnesses.

' CLARE H. DRAPER. Witnesses";

WENDELL WILLIAMS, BERTHA I. SNARE. 

